As portable electronic devices get smaller and smaller, the size of the functional components is forced to decrease. In addition, there is currently a demand for larger displays which enable a greater amount of information to be viewed at a given time. The combination of smaller devices and larger displays puts pressure on device manufacturers to reduce the size of loudspeakers. Unfortunately, little further size reduction can be achieved with conventional loudspeakers without sacrificing audio performance. At the moment, the performance is adequate for speech, but expectations are set to increase for music. With current mobile phones, the sound is often routed through the back or sides of the housing due to a lack of space on the front of the device, thereby compromising the audio performance further.
To overcome this issue, some manufacturers have started replacing conventional loudspeakers with integrated display speakers. With integrated display speakers, the display, the display cover, or the display and display cover in combination, serve as the loudspeaker diaphragm. In these devices, actuators are used to vibrate the display/cover to create pressure waves in the adjacent air. US2005/0226455A1 discloses a vibrating display; EP1617703A2, WO2006/038176A1 and WO2009/017278A1 disclose vibrating display covers; and EP1827057A2, GB2360901A and EP1912469A1 disclose vibrating display/display cover combinations.
Whilst integrated display speakers have demonstrated some success, they are not without problems. One such problem is associated with the reflection of light from the external surface of the display/cover. When the display/cover vibrates, reflections on the external surface also vibrate and distract the user, thereby having a negative influence on the quality of the displayed image. In particular, vibrations of the display/cover are more visible at low frequencies (<400 Hz) due to the large excursion at the centre of the display/cover.
Further development of integrated display speakers has led to the discovery of the distributed mode loudspeaker (DML). The DML is a flat panel display speaker in which sound is produced by inducing uniformly distributed vibration modes in a flexible display panel. This is in contrast to most other types of speaker which produce sound by inducing pistonic motion in the diaphragm. The advantages of DML speakers are that they are flat, they exhibit good frequency response provided that the panel is large enough, they are able to produce stereo sound from a single panel, and can achieve broad sound dispersion. However, these speakers also suffer from the above-mentioned reflection issue, and additionally, only work well with large panel displays (e.g. TV screens) where the vibration modes are so dense that the user does not notice them. As the display size is reduced, the density of vibration modes decreases, which results in greater distortion and a poorer frequency response.
Another issue with device loudspeakers is the directionality of the generated sound. In certain situations, a user may wish to use his phone in integrated hands free (IHF) or speakerphone mode. This situation may arise, for example, if the user wants to discuss on-screen content with another party during a telephone call. In this scenario, earpiece mode is impractical because holding the phone against the ear would prevent the user from viewing the display. In addition, the use of earphones may be inconvenient.
In IHF mode, a user might want the sound to exit the loudspeaker omnidirectionally so that other people are able to hear the audio output. This may be the case where the user is listening to music or involved in a conference call. In other situations, however, the user may prefer some privacy. For example, if the user is discussing sensitive or personal matters over the phone, he may not want other people in the vicinity to hear both sides of the conversation.
In all wave-producing sources, the directionality (or directivity) is dependent on the size of the source relative to the wavelengths generated. The larger the source with respect to the wavelength of the sound waves, the greater the directionality. Many current devices provide little directional discrimination because the sound exits the housing via small holes. One method of improving the directionality is therefore to increase the size of the source. With electronic devices, however, increasing the size of the loudspeaker inhibits miniaturisation of the device. The ability to control the directionality of the audio output in IHF mode without hindering miniaturisation of the device would therefore be advantageous.
The apparatus and associated methods disclosed herein may or may not address one or more of the issues described above.
The listing or discussion of a prior-published document or any background in this specification should not necessarily be taken as an acknowledgement that the document or background is part of the state of the art or is common general knowledge. One or more aspects/embodiments of the present disclosure may or may not address one or more of the background issues.